Add Null check at JacksonAllInObjectScope to avoid NullPointerException

[sakama]

TODO

• This PR depends on embulk-core: PageReader#get{String,Timestamp,Json} calls #isNull to return null embulk#654
  • Need to update Embulk version at build.gradle

Changes

I was trying to fix ArrayIndexOutOfBoundsException that happens with embulk-output-elasticsearch at #86 and revised it.
I tried embulk/embulk#654 and got NullPointerException instead of ArrayIndexOutOfBoundsException.
This should valid behavior. Then, I added Null check to JacksonAllInObjectScope#{string|timestamp|json}Column to avoid this failure.

Stacktrace

Caused by: java.lang.NullPointerException
	at org.embulk.spi.time.TimestampFormatter.format(TimestampFormatter.java:93)
	at org.embulk.base.restclient.jackson.scope.JacksonAllInObjectScope$1.timestampColumn(JacksonAllInObjectScope.java:74)
	at org.embulk.spi.Column.visit(Column.java:60)
	at org.embulk.spi.Schema.visitColumns(Schema.java:81)
	at org.embulk.base.restclient.jackson.scope.JacksonAllInObjectScope.scopeObject(JacksonAllInObjectScope.java:36)
	at org.embulk.base.restclient.jackson.scope.JacksonObjectScopeBase.scopeEmbulkValues(JacksonObjectScopeBase.java:17)
	at org.embulk.base.restclient.jackson.scope.JacksonObjectScopeBase.scopeEmbulkValues(JacksonObjectScopeBase.java:9)
	at org.embulk.base.restclient.record.ValueExporter.exportValueToBuildRecord(ValueExporter.java:14)
	at org.embulk.base.restclient.record.RecordExporter.exportRecord(RecordExporter.java:18)
	at org.embulk.base.restclient.RestClientPageOutput.add(RestClientPageOutput.java:43)
	at org.embulk.exec.LocalExecutorPlugin$ScatterTransactionalPageOutput$OutputWorker.call(LocalExecutorPlugin.java:394)
	at org.embulk.exec.LocalExecutorPlugin$ScatterTransactionalPageOutput$OutputWorker.call(LocalExecutorPlugin.java:319)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
	Suppressed: java.lang.NullPointerException
		... 16 more
	Suppressed: java.lang.NullPointerException
		... 16 more
	Suppressed: java.lang.NullPointerException
		... 16 more

[sakama]

Ah, this PR works without waiting embulk/embulk#654

No need to wait embulk/embulk#654

if (!singlePageRecordReader.isNull(column)) {
    resultObject.put(column.getName(),
                     singlePageRecordReader.getString(column));
}

Need to wait embulk/embulk#654

if (singlePageRecordReader.getString(column) != null) {
    resultObject.put(column.getName(),
                     singlePageRecordReader.getString(column));
}

[sakama]

@dmikurube How do you think about?

[dmikurube]

@sakama Sorry to be late. lgtm!

We may have an option to add null JSON values there as below, but it's not trivial which is better. Starting from this sounds good to me.

"some_empty_value": null

[dmikurube]

Merging this, and releasing a new version soon...

[sakama]

thanks!